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NASA NTRS1959

Boundary-Layer Transition on Hollow Cylinders in Supersonic Free Flight as Affected by Mach Number and a Screwthread Type of Surface Roughness

The effects of Mach number and surface-roughness variation on boundary-layer transition were studied using fin-stabilized hollow-tube models in free flight. The tests were conducted over the Mach number range from 2.8 to 7 at a nominally constant unit Reynolds number of 3 million per inch, and with heat transfer to the model surface. A screwthread type of distributed two-dimensional roughness was used. Nominal thread heights varied from 100 microinches to 2100 microinches. Transition Reynolds number was found to increase with increasing Mach number at a rate depending simultaneously on Mach number and roughness height. The laminar boundary layer was found to tolerate increasing amounts of roughness as Mach number increased. For a given Mach number an optimum roughness height was found which gave a maximum laminar run greater than was obtained with a smooth surface.

James, Carlton S.↗
NASA NTRS1996

Spectra of Baroclinic Inertia-Gravity Wave Turbulence

Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.

Glazman, Roman E.↗
NASA NTRS1997

Compensation for Spherical Geometric and Absorption Effects on Lower Thermospheric Emission Intensities Derived from High Earth Orbit Images

Remote sensing of the atmosphere from high earth orbit is very attractive due to the large field of view obtained and a true global perspective. This viewpoint is complicated by earth curvature effects so that slant path enhancement and absorption effects, small from low earth orbit, become dominant even at small nadir view angles. The effect is further complicated by the large range of local times and solar zenith angles in a single image leading to a modulation of the image intensity by a significant portion of the diurnal height variation of the absorbing layer. The latter effect is significant in particular for mesospheric, stratospheric and auroral emissions due to their depth in the atmosphere. As a particular case, the emissions from atomic oxygen (130.4 and 135.6 nm) and molecular nitrogen (two LBH bands, LBHS from 140 to 160 nm and LBHL from 160 to 180 nm) as viewed from the Ultraviolet Imager (UVI) are examined. The LBH emissions are of particular interest since LBHS has significant 02 absorption while LBHL does not, In the case of auroral emissions this differential absorption, well examined in the nadir, gives information about the height of the emission and therefore the energy of the precipitating particles. Using simulations of the viewing geometry and images from the UVI we examine these effects and obtain correction factors to adjust to the nadir case with a significant improvement of the derived characteristic energy. There is a surprisingly large effect on the images from the 02 diurnal layer height changes. An empirical compensation to the nadir case is explored based on the local nadir and local zenith angles for each portion of the image. These compensations are demonstrated as applied to the above emissions in both auroral and dayglow images and compared to models. The extension of these findings to other instruments, emissions and spectral regions is examined.

Swift, W.↗
NASA NTRS1995

Vertical Scales of Turbulence at the Mount Wilson Observatory

The vertical scales of turbulence at the Mount Wilson Observatory are inferred from data from the University of California at Berkeley Infrared Spatial Interferometer (ISI), by modeling path length fluctuations observed in the interferometric paths to celestial objects and those in instrumental ground-based paths. The correlations between the stellar and ground-based path length fluctuations and the temporal statistics of those fluctuations are modeled on various timescales to constrain the vertical scales. A Kolmogorov-Taylor turbulence model with a finite outer scale was used to simulate ISI data. The simulation also included the white instrumental noise of the interferometer, aperture-filtering effects, and the data analysis algorithms. The simulations suggest that the path delay fluctuations observed in the 1992-1993 ISI data are largely consistent with being generated by refractivity fluctuations at two characteristic vertical scales: one extending to a height of 45 m above the ground, with a wind speed of about 1 m/ s, and another at a much higher altitude, with a wind speed of about 10 m/ s. The height of the lower layer is of the order of the dimensions of trees and other structures near the interferometer, which suggests that these objects, including elements of the interferometer, may play a role in generating the lower layer of turbulence. The modeling indicates that the high- attitude component contributes primarily to short-period (less than 10 s) fluctuations, while the lower component dominates the long-period (up to a few minutes) fluctuations. The lower component turbulent height, along with outer scales of the order of 10 m, suggest that the baseline dependence of long-term interferometric, atmospheric fluctuations should weaken for baselines greater than a few tens of meters. Simulations further show that there is the potential for improving the seeing or astrometric accuracy by about 30%-50% on average, if the path length fluctuations in the lower component are directly calibrated. Statistical and systematic effects induce an error of about 15 m in the estimate of the lower component turbulent altitude.

Treuhaft, Robert N.↗
NASA NTRS1998

Calculation of Tip Clearance Effects in a Transonic Compressor Rotor

The flow through the tip clearance region of a transonic compressor rotor (NASA rotor 37) was computed and compared to aerodynamic probe and laser anemometer data. Tip clearance effects were modeled both by gridding the clearance gap and by using a simple periodicity model across the ungridded gap. The simple model was run with both the full gap height, and with half the gap height to simulate a vena-contracta effect. Comparisons between computed and measured performance maps and downstream profiles were used to validate the models and to assess the effects of gap height on the simple clearance model. Recommendations were made concern- ing the use of the simple clearance model Detailed comparisons were made between the gridded clearance gap solution and the laser anemometer data near the tip at two operating points. The computed results agreed fairly well with the data but overpredicted the extent of the casing separation and underpredicted the wake decay rate. The computations were then used to describe the interaction of the tip vortex, the passage shock, and the casing boundary layer.

Chima, R. V.↗
NASA NTRS1998

Magnetic Field Configuration of Active Region NOAA 6555 at the Time of a Long Duration Flare on 23 March 1991: An Exception to Standard Flare Reconnection Model

The high-resolution H(sub alpha) images observed during the decay phase of a long duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas, all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long duration flare was observed in the region of low magnetic shear at the photosphere. The H(sub alpha) loop activity started soon after the maximum phase of the flare. There were few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45 deg with the east-west axis. Gradually, increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue-shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to the chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H(sub alpha) loops. The height of the H(sub alpha) loops were derived by comparing them with the computed field lines. From the temporal evolution of the H(sub alpha) loop activity, we derive the negative rate of appearance of H(sub alpha) features as a function of height. It is found that the field lines oriented along one of the neutral lines was sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long duration flare.

Choudhary, Debi Prasad↗
NASA NTRS1999

TRMM Precipitation Radar Reflectivity Profiles Compared to High-Resolution Airborne and Ground-Based Radar Measurements

In this paper, TRMM (Tropical Rainfall Measuring Mission Satellite) Precipitation Radar (PR) products are evaluated by means of simultaneous comparisons with data from the high-altitude ER-2 Doppler Radar (EDOP), as well as ground-based radars. The comparison is aimed primarily at the vertical reflectivity structure, which is of key importance in TRMM rain type classification and latent heating estimation. The radars used in this study have considerably different viewing geometries and resolutions, demanding non-trivial mapping procedures in common earth-relative coordinates. Mapped vertical cross sections and mean profiles of reflectivity from the PR, EDOP, and ground-based radars are compared for six cases. These cases cover a stratiform frontal rainband, convective cells of various sizes and stages, and a hurricane. For precipitating systems that are large relative to the PR footprint size, PR reflectivity profiles compare very well to high-resolution measurements thresholded to the PR minimum reflectivity, and derived variables such as bright band height and rain types are accurate, even at high PR incidence angles. It was found that for, the PR reflectivity of convective cells small relative to the PR footprint is weaker than in reality. Some of these differences can be explained by non-uniform beam filling. For other cases where strong reflectivity gradients occur within a PR footprint, the reflectivity distribution is spread out due to filtering by the PR antenna illumination pattern. In these cases, rain type classification may err and be biased towards the stratiform type, and the average reflectivity tends to be underestimated. The limited sensitivity of the PR implies that the upper regions of precipitation systems remain undetected and that the PR storm top height estimate is unreliable, usually underestimating the actual storm top height. This applies to all cases but the discrepancy is larger for smaller cells where limited sensitivity is compounded by incomplete beam filling. Users of level three TRMM PR products should be aware of this scale dependency.

Heymsfield, G. M.↗
NASA NTRS1968

Data Acquisition and Prompt Analysis System for High Altitude Balloon Experiments

An inexpensive and simple data acquisition system has been developed for balloon borne experiments and has been tested with a gamma ray detector in a balloon flight launched from Palestine, Texas. The detector used for the test consisted of an NaI(T1) scintillation crystal encased in a 1/8 in. plastic scintillator-charged particle shield. The combination was viewed by a single photomultiplier and charged particle gating was accomplished by a conventional phoswich discriminator. The pulse height analysis of the NaI events, not associated with prompt charged particle interactions, is accomplished by converting to a time spectrum using an airborne height to time converter. A range of pulse widths from 5 microseconds to 250 microseconds corresponds to energy losses in NaI from 100 to 1000 keV. The time spectrum information, along with charged particle events and barometric pressure, is fed to a mixer which modulates a 252.4 Mc FM transmitter. The original scintillator spectrum is recovered on the ground utilizing conversion circuitry at the receiver video output and a 128 channel commercial pulse height analyzer. The charged particle events of standard time width are stored with the spectrum at a fixed channel position and are therefore represented by a sharp line riding on the lower part of the NaI energy loss spectrum. An energy loss greater than 1000 keV is presented by the maximum pulse width of the converter and stored in the last analyzer channel. Barometric pressure data is transmitted by low frequency modulation of the sme FM carrier. In flight operation, the receiver video output can be recorded on a wide band tape recorder and simultaneously analyzed by the 128 channel analyzer, or the telemetered data can be analyzed later. The flight system features high pulse resolution, essentially instantaneous time response, high data rate, and flexibility; and is of modest cost. A detailed description of the system and operating performance is discussed.

Sarkady, A. A.↗
NASA NTRS2000

Autonomous, Full-Time Cloud Profiling at Arm Sites with Micro Pulse Lidar

Since the early 1990's technology advances permit ground based lidar to operate full time and profile all significant aerosol and cloud structure of the atmosphere up to the limit of signal attenuation. These systems are known as Micro Pulse Lidars (MPL), as referenced by Spinhirne (1993), and were first in operation at DOE Atmospheric Radiation Measurement (ARM) sites. The objective of the ARM program is to improve the predictability of climate change, particularly as it relates to cloud-climate feedback. The fundamental application of the MPL systems is towards the detection of all significant hydrometeor layers, to the limit of signal attenuation. The heating and cooling of the atmosphere are effected by the distribution and characteristics of clouds and aerosol concentration. Aerosol and cloud retrievals in several important areas can only be adequately obtained with active remote sensing by lidar. For cloud cover, the height and related emissivity of thin clouds and the distribution of base height for all clouds are basic parameters for the surface radiation budget, and lidar is essetial for accurate measurements. The ARM MPL observing network represents the first long-term, global lidar study known within the community. MPL systems are now operational at four ARM sites. A six year data set has been obtained at the original Oklahoma site, and there are several years of observations at tropical and artic sites. Observational results include cloud base height distributions and aerosol profiles. These expanding data sets offer a significant new resource for cloud, aerosol and atmospheric radiation analysis. The nature of the data sets, data processing algorithms, derived parameters and application results are presented.

Spinhirne, James D.↗
NASA NTRS1999

Stratospheric Impact of 1D-Variation Assimilation of TOVS/ATOVS Data

This paper will present an assessment of the impact to the stratospheric circulation of the DAO-GEOS2 (Data Assimilation Office -Goddard Earth Observing System) attributable to an improved 1D-Variational retrieval of heights. The assimilated heights are retrieved from both the TOVS (TIROS Operational Vertical Sounder) and the ATOVS (Advanced TOVS) sounders. Each sounder's sensitivity to temperature changes in the stratosphere will be addressed and its relationship to the model's background flow evaluated. Also detailed are the steps to ensure the quality of the data being assimilated. Finally the temporal and spatial scales, important to the stratospheric mean flow, will be evaluated in terms of the DAO-GEOS2 response to the assimilated heights.

Rokke, Laurie↗
NASA NTRS1999

Landscape-Scale Canopy Complexity in and Near Braulio Carillo National Park, Costa Rica

Using medium-large footprint lidar sampling of approximately 500 square km of Costa Rica, we assessed the vertical and horizontal complexity of a forest-dominated tropical landscape. As expected, vertical extents of structure and canopy heights estimated from lidar waveforms were smaller in high elevation forests than in forests at lower elevations. In areas of the park and long-protected areas of La Selva Biological Station, forests typically had more consistent ratios of median height to total height than areas with other types of recent land use. Areas outside the park exhibited both stronger and weaker spatial correlations in canopy properties than most areas within the park. We also simulated the effects of these differences on data products gridded from lidar transects, like those produced by the Vegetation Canopy Lidar (VCL) Mission.

Knox, Robert G.↗
NASA NTRS1999

Experimental Confirmation of Powerstick Concept

The results relating to the development and testing of the miniature Radioisotope Thermoelectric Generator (RTG)-like Powerstick (PS) device are presented. They confirm the earlier ideas and predictions regarding possible manufacturing of PS-devices. PS is based on a 238-Pu standard Radioactive Heating Unit (RHU) with thermal power 1.1 W developed and manufactured by DOE and successfully being used on spacecraft (Galileo, Cassini, e. g.). In the course of development, several design approaches were explored and achieving high PS efficiencies was considered. Better thermal insulation material (with thermal conductivity 0.02 W/mK) has been developed and used and different designs of PS were evaluated. Two types of PS were manufactured: PS-1, on the basis of one RHU and one thermoelectric battery/converter (TEB), and PS-2, on the basis of two RHU and one TEB. Two different sizes of TEB were used: first - with the legs of cross-section 0.45x0.45 sq-mm and height 35 mm, and second - with the legs of cross-section 0.6Ox0.60 sq-m and height 35 mm. In both cases, the number of legs was 400. The electrical power of the PS-1 was observed to deliver 22 mW at 2.5 V and for PS-2 - 53 mW at 4.1 V. The analysis of results showed that optimized version of PS-2 should be capable of more than 70 mW at 5 V, on the basis of TEB with legs of cross-section 0.67x0.67 sq-mm and height 40 mm with number of legs 324.

Pustovalov, A.↗
NASA NTRS2000

Estimating Forest Vertical Structure from Multialtitude, Fixed-Baseline Radar Interferometric and Polarimetric Data

Parameters describing the vertical structure of forests, for example tree height, height-to-base-of-live-crown, underlying topography, and leaf area density, bear on land-surface, biogeochemical, and climate modeling efforts. Single, fixed-baseline interferometric synthetic aperture radar (INSAR) normalized cross-correlations constitute two observations from which to estimate forest vertical structure parameters: Cross-correlation amplitude and phase. Multialtitude INSAR observations increase the effective number of baselines potentially enabling the estimation of a larger set of vertical-structure parameters. Polarimetry and polarimetric interferometry can further extend the observation set. This paper describes the first acquisition of multialtitude INSAR for the purpose of estimating the parameters describing a vegetated land surface. These data were collected over ponderosa pine in central Oregon near longitude and latitude -121 37 25 and 44 29 56. The JPL interferometric TOPSAR system was flown at the standard 8-km altitude, and also at 4-km and 2-km altitudes, in a race track. A reference line including the above coordinates was maintained at 35 deg for both the north-east heading and the return southwest heading, at all altitudes. In addition to the three altitudes for interferometry, one line was flown with full zero-baseline polarimetry at the 8-km altitude. A preliminary analysis of part of the data collected suggests that they are consistent with one of two physical models describing the vegetation: 1) a single-layer, randomly oriented forest volume with a very strong ground return or 2) a multilayered randomly oriented volume; a homogeneous, single-layer model with no ground return cannot account for the multialtitude correlation amplitudes. Below the inconsistency of the data with a single-layer model is followed by analysis scenarios which include either the ground or a layered structure. The ground returns suggested by this preliminary analysis seem too strong to be plausible, but parameters describing a two-layer compare reasonably well to a field-measured probability distribution of tree heights in the area.

Treuhaft, Robert N.↗
NASA NTRS2000

Phase Screen Determination for the GeoSAR Interferometric Mapping Instrument

GeoSAR is a dual frequency airborne radar interferometric mapping instrument designed to obtain high resolution and high accuracy digital elevation models. The X-band inteferometric antennas are mounted beneath the fuselage with a separation distance of 2.6 m. Midway between the antennas along the aircraft centerline is a large fairing housing the Laser Baseline metrology System (LBMS) and Inertial Navigtion Units (INUs). The P-band antennas are mounted in wingtip pods approximately 10 m from the aircraft centerline. Multipath signals reflected from the LBMS fairing cause phase distortions corrupting the topograhic height measurements for both the X-band and P-band systems. In addition multipath off the wing affects the P-band phase measurements. In this paper we discuss a technique used to mitigate the amount of X-Band multipath and methods calibrating and correcting the phase for both X-Band and P-Band using a high accuracy DEM. Height differences between the interferometrically derived elevations and a photogrammetrically derived DEM are converted into phase differences. Multipath phase errors are sinusoidal with spatial frequency and amplitude related to the magnitude of reflection of the multipath reflection point and its distance from the interferometric antennas. These phase residuals are fitted using a Chebyshev polynomial sequence and used as a phase screen in the processor to correct the phase prior to height reconstruction. Based on the correction signal it is possible to estimate the location and magnitude of the multipath signal. This information can then be used to extend the domain of the phase screen over mapping angles not covered during the calibration passes. Keywords: SAR,interferometry,phase screen

Hensley, Scott↗
NASA NTRS2000

Shock Formation of Slow Magnetosonic Waves in Coronal Plumes

We investigate the height of shock formation in coronal plumes for slow magnetosonic waves. The models take into account plume geometric spreading, heat conduction, and radiative damping. The wave parameters as well as the spreading functions of the plumes and the base magnetic field strengths are given by empirical constraints mostly from Solar and Heliospheric Observatory (SOHO)/ Ultraviolet Coronograph Spectrometer (UVCS), Extreme Ultraviolet Imaging Telescope (EIT), Michelson Doppler Imager (MDI), and Large Angle Spectrometric Coronagraph (LASCO). Our models show that shock formation occurs at relatively low coronal heights, typically within 1.2 RsuN, depending on the model parameters. The shock formation is calculated using the well-established wave breaking criterion given by the intersection of C+ characteristics in the space-time plane. Our models show that shock heating by slow magnetosonic waves is expected to be relevant at most heights in solar coronal plumes, although such waves are probably not the main energy supply mechanism.

Cuntz, Manfred↗
NASA NTRS2000

Lidar Technology at the Goddard Laser and Electro-Optics Branch

The Laser and Electro-Optics Branch at Goddard Space flight Center was established about three years ago to provide a focused center of engineering support and technology development in these disciplines with an emphasis on spaced based instruments for Earth and Space Science. The Branch has approximately 15 engineers and technicians with backgrounds in physics, optics, and electrical engineering. Members of the Branch are currently supporting a number of space based lidar efforts as well as several technology efforts aimed at enabling future missions. The largest effort within the Branch is support of the Ice, Cloud, and land Elevation Satellite (ICESAT) carrying the Geoscience Laser Altimeter System (GLAS) instrument. The ICESAT/GLAS primary science objectives are: 1) To determine the mass balance of the polar ice sheets and their contributions to global sea level change; and 2) To obtain essential data for prediction of future changes in ice volume and sea-level. The secondary science objectives are: 1) To measure cloud heights and the vertical structure of clouds and aerosols in the atmosphere; 2) To map the topography of land surfaces; and 3) To measure roughness, reflectivity, vegetation heights, snow-cover, and sea-ice surface characteristics. Our efforts have concentrated on the GLAS receiver component development, the Laser Reference Sensor for the Stellar Reference System, the GLAS fiber optics subsystems, and the prelaunch calibration facilities. We will report on our efforts in the development of the space qualified interference filter [Allan], etalon filter, photon counting detectors, etalor/laser tracking system, and instrument fiber optics, as well as specification and selection of the star tracker and development of the calibration test bed. We are also engaged in development work on lidar sounders for chemical species. We are developing new lidar technology to enable a new class of miniature lidar instruments that are compatible with small Discovery-class orbiters now in the NASA planetary program. The purpose of the lidar is to continuously profile the water vapor and dust in the Mars atmosphere from orbit in order to quantify its dynamics, their relationship in the diurnal cycles, and to infer water vapor exchange with the Mars surface. To remotely measure the water-vapor height profiles, we will use the differential absorption lidar (DIAL) technique. We are also developing a laser sensor for measuring the total column content of CO2 in the atmosphere of the earth. CO2 is the principal greenhouse gas and has increased by roughly 80 ppm in the last century and a half. We will report our efforts in the development of the laser transmitter and photon counting detector components for a Mars Orbiting DIAL system and for the CO2 sounder.

Heaps, William S.↗
NASA NTRS2000

Morphology of Mars North Polar Ice Cap

The northern ice cap of Mars consists of a parabolic dome centered within 13 km of the pole, plus an arm-like ridge extending from the dome between about 135 and 225 east. Chasma Boreale lies between the dome and the extended ridge. The base of the dome is approximately elliptical with a major axis of 1100 km along the 90 east to 270 east direction and minor axis of 700 km along zero east to 180 deg. The heights of the dome and the extended ridge are respectively 2900 inches and 1700 inches above the surrounding basin. Least-squares fitting of a parabola through height profiles of the dome along longitudes 90 deg to 270 deg and zero deg to 180 deg gives an elliptic-paraboloid equation for the dome: Z(m) = 2800 - [(X-x)(exp 2)/113.6] - [(Y-y)(exp 2)/50.3], where X is the 90 deg to 270 deg axis, x = 9.90 km, y = 13.32 km, and the slightly-different fitted heights for the two axes are averaged. The center of the dome is shifted 13.32 km from the pole along zero deg longitude and 9.90 km along 90 deg longitude. Typical mean surface slopes on the ice cap are the order of 1/100 (0.6 deg), A small central portion of the cap, about 100 km by 200 km, extends in elevation about 200 inches above the parabolic shape of the cap. Additional information is contained in the original extended abstract.

Zwally, H. J.↗
NASA NTRS2001

Shock Formation of Slow Magnetosonic Waves in Coronal Plumes

We investigate the height of shock formation in coroner plumes for slow magnetosonic waves. The models take into account plume geometric spreading, heat conduction and radiative damping. The wave parameters as well as the spreading functions of the plumes and the base magnetic field strengths are given by empirical constraints mostly from Solar and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer (SOHO/UVCS). Our models show that shock formation occurs at low coronal heights, i.e., within 1.3 solar radius, depending on the model parameters. The shock formation is calculated using the well-established wave breaking condition given by the intersection of C+ characteristics in the space-time plane. Our models show that shock heating by slow magnetosonic waves is expected to be relevant at most heights in solar coronal plumes, although slow magnetosonic waves are most likely not a solely operating energy supply mechanism.

Cuntz, Manfred↗